Various glucarolactone-based compounds, including calcium glucarate (CGT), micro-encapsulated D-glucaro-1,4-lactone, potassium hydrogen glucarate and 2,4-di-O-acetyl-D-glucaro-1,4-lactone, are known to be effective as inhibitors of beta-glucuronidase in cells, blood, urine and in the intestine and liver. By inhibiting beta-glucuronidase, less detoxified (that is glucuronidated) toxins are hydrolysed and therefore more toxins are excreted. As a result, such glucarolactone-based compounds are useful in the treatment and prevention of various types of cancer.
Recently glucarate in the sustained release dietary form of calcium glucarate, was found to be a potent chemopreventative agent in the rodent system as having preventative activity against chemical carcinogenesis (both initiation and promotion phases) in the liver, Oredipe, O. A., et al., Effects of calcium glucarate on the promotion of diethylnitrosamine-initiated altered hepatic foci in rats in Cancer Letters 38: 95-99 (1987); lung, Walaszek, Z., et al., Dietary glucarate-mediated reduction of sensitivity of murine strains to chemical carcinogenesis in Cancer Letters 33: 25-32 (1986); skin, Dwivedi, C., et al., Modulation of chemically initiated and promoted skin tumorigenesis in CD-1 mice by dietary glucarate in J. Environ. Pathol. Toxicol. and Oncol., in press; and mammary gland, Walaszek, Z., et al., Dietary glucarate as anti-promoter of 7,12-dimethylbenz(a)anthracene-induced mammary tumorigenesis in Carcinogenesis, 7: 1463-1466 (1986). See, also for example, Walaszek, Z. et al. Inhibition of 7,12-dimethylbenzanthracene-induced rat mammary tumorigenesis by 2,5-di-0-acetyl-D-glucaro-1,4:6,3-dilactone, an in-vivo beta-glucuronidase inhibitor. Carcinogenesis 5: 767-772, (1984); and, Walaszek, Z., et al., Inhibition of N-methyl-N-nitrosourea-induced mammary tumorigenesis in the rat by a beta-glucuronidase inhibitor. IRCS Medical Science 14: 677-678, (1986).
In Walaszek et al., Carcinogenesis 7, supra, preliminary evidence was obtained that glucarate also inhibits and indeed causes regression of DMBA-induced rat mammary tumors. Glucarate is a normal body constituent, as it is the end product of glucuronic acid metabolism which is excreted in the urine. However, glucarate is present in blood and tissues at very low levels. Glucarate is non-toxic in dosages up to 10% in the diet as calcium glucarate and is effective at dietary levels of 4% (128 mmol/kg diet). In the systems studied to date it has been indicated that the active component is glucarate. Glucarate can undergo equilibrium formation of D-glucaro-1,4-lactone. Through inhibition of beta-glucuronidase, the lactone effects net formation of glucuronide conjugates of certain carcinogens or promoting agents in the phase II detoxification reactions, Dwivedi, C., et al., Net glucuronidation in different rat strains: Importance of microsomal beta-glucuronidase. The FASEB Journal, 1: 303-307 (1987).
Retinoid-based compounds including retinylacetate, retinylmethyl ether, 13-cis-retinoic acid and N-(4-hydroxyphenyl) retinamide (HPR), have similarly been investigated for their anticarcinogenic activity. These retinoids, both natural and synthetic, have been under intensive investigation as both cancer chemopreventative agents and anti-cancer (chemotherapeutic) agents, Moon, R. C., et al., Retinoids and cancer. In Sporn, M. B., Roberts, A. B., Goodman, D. S. eds., The retinoids, Vol 2. New York: Academic Press, 327-371 (1984) and Thompson, H. J., et al., Comparative review of the efficacy of a polyamine antimetabolite retinoids and selenium. J. Natl. Cancer Inst. 77: 595-598 (1986). Retinoids have been shown to be very effective at or near toxic levels in several experimental animal systems including MNU, Moon, R. C., et al., Retinylacetate inhibits mammary carcinogenesis induced by N-methyl-N-nitrosourea, Nature 267: 620-621 (1977); and the 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumor system, Abou-Issa, H., et al., Anticarcinogenic effect of retinoids on 7,12-dimethylbenz(a)anthracene-induced mammary tumor induction, and its relationship to cyclic AMP-dependent protein kinase, Biochem. Biophys. Res. Commun., 135: 116-123 (1986). Many of the toxicity problems were minimized in protocols associated with mammary carcinogenesis with the introduction of the synthetic retinoid N-(4-hydroxyphenyl)retinamide which displays trophism for the mammary gland, Moon, R. C., et al., N-4-Hydroxyphenyl retinamide, a new retinoid for preventing breast cancer in the rat, Cancer Res. 39: 1339-1349 (1979). This compound is currently being tested clinically in combination with the anti-estrogen Tamoxifen.RTM., in the prevention of breast cancer in women at risk, Rustin, G. J. S., et al., The potential use of retinoids in oncology (Meeting Report). Brit. J. Cancer 51: 443-445 (1985). [See also, Abou-Issa, H., et al., Anti-carcinogenic effect of retinoids on 7,12-dimethylbenz(a)anthracene-induced mammary tumor formation and its relation to cyclic AMP-dependent kinase Biochem. Biophys. Res. Commun. 135: 116-123, (1986); Welsch, C. W., et al., Retinoids and Mammary gland tumorigenesis in Diet, Nutrition and Cancer (B. S. Reddy and L. A. Cohen eds.) CRS Press Boca Raton, FL. pp 1-21, (1986); Schamberger, R. J. Chemoprevention of cancer in Diet, Nutrition and Cancer. (B. S. Reddy and L. A. Cohen eds.) CRC Press, pp. 43-62, (1986); and, Moon, R. C., Inhibition of 7,12-dimethylbenzanthracene-induced mammary carcinogenesis by retinyl acetate. Cancer Res. 36: 2626, (1976).]
These studies confirmed the activity of relatively high doses of retinoids against the chemical induction of mammary carcinogenesis in the rat. Similarly, high dosages were tested against the chemical carcinogen-mediated induction of tumors in the mammary gland, lung, skin, intestine and liver. Further, retinoids have been shown to protect skin, nasopharnyx, lower respiratory tract, urinary bladder and colon against carcinogens. In addition, these retinoic acid analogs (Vitamin A active compounds) have been tested in combination with the micronutrient selenium.
One problem associated with the use of retinoid-based compounds is that relatively high doses of the retinoids must be administered in order to achieve the desired anticarcinogen effect. Such high doses of retinoids often results in cummulative toxicity, with the excess retinoids being deposited in the liver.
Because relatively high levels of around 4% of dietary calcium glucarate are required for maximum effectiveness, and because of potential retinoid toxicity and the desire to increase the therapeutic index, the combination of the retinoid and glucarate was disclosed in the parent patent application Ser. No. 089,568. Surprisingly, when low ineffective dosages (approximately one-half the effective dose or less) of HPR and CGT were combined in the diet, they interacted synergistically to inhibit carcinogenesis to the extent of high effective dosages of either agent alone. The results of this patent application were later reported in Abou-Issa, H. M., et al., Putative metabolites derived from dietary combinations of calcium glucarate and N-(4-hydroxyphenyl)retinamide act synergistically to inhibit the induction of rat mammary tumors by 7,12-dimethylbenz(a)anthracene. Proc. Natl. Acad. Sci. (U.S.) 85: 4181-4184 (1988). This combination has now been further evaluated as a chemotherapeutic agent on established DMBA-induced rat mammary tumors. The results disclosed herein indicate that the combination of the retinoid and the glucarate also interact synergistically to inhibit rat mammary tumor growth.
There has been no suggestion in the art that a combination of glucarolactone-based compounds and retinoid-based compounds would be especially useful as anticarcinogens; that is, that the combination of these compounds would represent an alternative for use in the prevention of cancer or for use in the therapeutic treatment of cancer.
It has now been found that the use of a combination of glucarolactone-based compounds and retinoid-based compounds or their pharmaceutically-acceptable salts and esters, compounds which are known to be safely administered to humans and animals, significantly inhibit tumor growth and to shrink tumors.
It is therefore an object of the present invention to provide a safe and effective dietary supplement and method for inhibiting tumor growth and for reducing the incidence of cancer in certain high risk populations.
Other objects and advantages of the invention will be apparent from the following detailed description of the invention.